BACKGROUND: To address limitations and challenges associated with current health surveillance of people with intellectual and developmental disabilities (IDD), this study investigates the use of all-payer claims data to identify and characterise this population. METHOD: All-payer claims data from 2010 to 2014 were used to study people with IDD in New Hampshire. Starting with the Centers for Medicare and Medicaid Services' algorithm, IDD was defined using ICD-9 diagnosis codes. Additional ICD-9 codes for developmental disabilities were included to build the knowledge base begun by recent research conducted on Medicaid claimants in five other states. RESULTS: Findings showed the enhanced algorithm offers a replicable and feasible way to conduct health surveillance of people with IDD at the state level. CONCLUSION: Substantive and significant differences between Medicaid and commercial claimants suggest that using all-payer claims provides a richer and more complete method for health surveillance of people with IDD.